1. Field of the Invention
The present invention relates to an image sensor and a method of manufacturing the same.
2. Background of the Related Art
Recently, with a rapid development of the electric/electronic technologies, various electronics, such as video cameras, digital still cameras, minicam adapted personal computers (PC), minicam adapted mobile phones and so forth, employing image sensor technologies have been widely developed and used.
Traditionally, in a conventional image sensor, a charge coupled device (CCD) has been generally used. However, such CCD has drawbacks in high driving voltage, a separate additional support circuit, and high per-unit prices, so that the usage thereof has been on the decrease presently.
Recently, as an image sensor for overcoming the disadvantages of the CCD, attention is attracted to a Complementary Metal Oxide Semiconductor (CMOS) image sensor. Since the CMOS image sensor is manufactured based on CMOS circuit technologies, it, contrary to the existing CCD, has advantages in that it can be driven with low voltage, it does not require an additional support circuit, it has a low per-unit price and so on.
In U.S. Pat. No. 6,191,409, entitled “Image sensor having means for changing predetermined voltage”, and U.S. Pat. No. 5,710,446, entitled “Active pixel sensor cell that utilizes a parasitic transistor to reset the photodiode of the cell”, examples of CMOS image sensors are represented.
As illustrated in FIG. 1, the prior art CMOS image sensor is formed in an active region of a semiconductor substrate 1, wherein the active region is defined by an isolation 2. The CMOS image sensor includes a photodiode 3 for generating and accumulating photo electrons, and a signal processing transistor 10 for transmitting and emitting photo electrons accumulated in the photodiode 3 to an image processing circuit (not illustrated) Here, the signal processing transistor 10 includes, for example, gate insulating film pattern 11, gate electrode pattern 12, spacer 13, and impurity region 14.
As illustrated in FIG. 1, in the prior art, an impurity region 3a is formed all over a prearranged photodiode region of the semiconductor substrate 1, and a depletion region (DR) is formed during the operation of the sensor. In this case, the impurity region 3a includes, for example, n-type impurity (shown as N+ in the drawings).
Also as shown in FIG. 1, the depletion region (DR) extends toward an inner portion of the semiconductor substrate 1, and is not exposed at the surface of the semiconductor substrate 1. As a result, among the incident lights that are directed to the photodiode 3, only the light with a long enough wavelength L1, for example red light and green light, can reach the depletion region (DR) located deep inside the semiconductor substrate 1, and the light with a short wavelength L2, for example blue light, can't reach the depletion region (DR).
As a result, without any additional complementary measures, the photodiode 3 can perform the generation/accumulation of photo electrons only by absorbing the light with the long enough wavelength L1, for example red light and green light, which reaches the depletion region (DR). And, the photodiode 3 cannot properly perform the generation/accumulation of photo electrons by absorbing the light with the short wavelength L2, for example blue light, which does not reach the depletion region (DR). Thus, the image sensor according to the prior art has a poor quality in color presentation.